Acer Aspire LA-7912P Rev.1.0 - brak zasilania SPI, diody LED włączają się na ok 3s

Cześć.

Mam na stole starego laptopa Acer Aspire (nie wiem dokładnie jaki model, bo wszystkie naklejki już dawno zniknęły). Chciałbym go uruchomić, natomiast on nie bardzo tego chce — włączają się diody, cooler delikatnie drgnie i po około 3 sekundach wszystko gaśnie.

Płyta główna to LA-7912P Rev.:1.0

Napięcie na głównej linii zasilania = 19,25V (podawane z oryginalnego zasilacza)
Napięcie na 8 nodze SPI (U36) = 0V (w ciągu tych 3s pozornego uruchomienia także). Rezystancja, względem masy, na tej nodze = 40kΩ

Pomierzyłem także cewki. Wyniki podaję w kolejności - oznaczenie cewki, rezystancja względem masy, napięcie na cewce przy wyłączonej płycie, napięcie na cewce przy pozornie włączonej płycie:
- PL9, 10Ω, 0V, 0V
- PL22, 1,1Ω, 0V, 0V
- PL21, 1,4Ω, 0V, 0V
- PL20, 1,4Ω, 0V, 0V
- PL14, 6,8Ω, 0V, 0V
- PL25, 79Ω, 0V, 0V
- PL7, 35Ω, 5V, 5V
- PL6, 570Ω, 3.3V, 3.3V
- PL15, 5Ω, 0V, 0V
- PL4, R≥20MΩ, 3V, 3V
- PL27, 29Ω, 0V, 0V

Martwi mnie brak zasilania SPI i jednocześnie zastanawia, że rezystancje na prawie wszystkich cewkach są dość niskie.

Co mogę sprawdzić, aby spróbować zdiagnozować tę płytę?

matic ha scritto:The resistance measurements on the coils must be wrong, or you have a damaged meter.

It also seemed suspicious to me, that's why I measured several times. And it didn't want to come out differently. Now, after these a few hours, I measured them all again and a few differences came out:
- PL9, 432Ω
- PL22, 1,1Ω
- PL21, 1,4Ω
- PL20, 1,4Ω
- PL14, 6,8Ω
- PL25, 79Ω
- PL7, 12kΩ
- PL6, 1,4kΩ
- PL15, 5Ω
- PL4, R≥20MΩ
- PL27, 103Ω
What could such a situation come from?

matic ha scritto:Did you measure the resistances with the power supply and main battery disconnected from the board?

Both power sources were and are disconnected.

I must add that with these previous measurements I got advice to look around PL7 because it is far too low resistance. Before I measured the coil again, I checked the PQ17 and PQ19 transistors:

PQ17 - only 1.7Ω in both directions between the gate and the source. In the diode test, it also shows a short circuit.
PQ17 - high resistances everywhere. Diode test - it's hard to say. Once a full short-circuit between drain and source. But only one way. After a while, with the next measuring short circuit there is no longer. As if the transistor "opened" with measuring and "closed" in a moment.

matic ha scritto:What about another multimeter?
Before processing, we must make sure the measurements are correct, as further diagnosis is based on them.

It took a while but I managed to give a different multimeter. I compared the readings and coincide with these:

bpjl ha scritto:- PL9, 432Ω
- PL22, 1,1Ω
- PL21, 1,4Ω
- PL20, 1,4Ω
- PL14, 6,8Ω
- PL25, 79Ω
- PL7, 12kΩ
- PL6, 1,4kΩ
- PL15, 5Ω
- PL4, R≥20MΩ
- PL27, 103Ω

The switched off board takes 7mA. After turning on the consumption increases to 16ma. When the board goes out, the current remains at 14-15mA.

I borrowed, for this afternoon, the same, working board, with a working CPU. I measured the coils and parameters on the 8th leg to have a comparison.



An working board has no dedicated GPU therefore there is no PL25 and PL27. SPI voltage appears when the board is turned on.